The present invention relates to water-thinnable polyester coatings and more particularly to suppression of solvent popping and elimination of volatile organic co-solvent in such coatings formulations.
It is known to formulate aqueous coatings of polyester resins and aminoplast cross-linking resins such as are described in U.S. Pat. No. 3,463,750. In such coatings, however, the polyester polymer typically can only be dispersed or diluted in water with the aid of volatile organic co-solvent. These co-solvents volatilize during heat-curing operations which can create pollution and cause solvent "pops" in the cured film. Also, such co-solvents lower the effective non-volatile solids content of the coatings which makes such coatings less efficient and economic in commercial use. In particular, U.S. Pat. No. 3,463,750 proposes water-thinnable polyester resins made from the condensation product of a polybasic acid (e.g. trimellitic acid), an unsaturated or saturated dibasic acid (e.g. maleic acid), a polyol (e.g. trimethylolpropane), and an allyl ether of a polyhydric alcohol having at least three hydroxyl groups (e.g. trimethylolpropane-diallyl ether). The coatings described in this citaton require at least about 8 to 11% or more volatile organic co-solvent in the examples for adequately dispersing the polyester resin in water and stabilizing such polyester thereafter. Further on this citation can be found in the examples which follow.
The present invention substantially suppresses solvent popping in the cured film and can obviate the necessity of using such volatile organic co-solvents by providing a unique blend of a polyester resin with disclosed allyl ether alcohols which not only function as conventional co-solvents but also are cross-linkable into the coating upon subsequent curing operations. Higher non-volatile solids content, reduced pollution, and superior performance coatings are thereby obtained.